Valve seats, ball seats, ratchets and racks that require high resistance to corrosion and impact are made of Cu-infiltrated sintered Fe-base alloys which are produced by the following procedure:
(1) preparing a powder mix providing a single or double formulation (in order to produce a sintered material having both high wear resistance and good toughness); PA0 (2) pressing the mix into a compact of a single phase (if the mix has a single formulation) or a double phase (in upper and two layers if the mix has a double formulation); PA0 (3) sintering the compact by holding it in vacuum or a non-oxidizing atmosphere at a temperature in the range of 1050.degree. to 1200.degree. C.; PA0 (4) placing the sintered compact on or under a separately prepared compact of an infiltrant primarily consisting of Cu powder or Cu alloy powder; and PA0 (5) holding the assembly in vacuum or non-oxidizing atmosphere at a temperature in the range of 1100.degree. to 1200.degree. C. so that the infiltrant enters and closed open pores in the sintered compact. PA0 (1) preparing two powder mixes, one having a predetermined formulation with a powder of an infiltrating material, preferably in an amount of 10 to 40 wt. %, that contains Cu powder or Cu alloy powder as the primary component, and the other having a predetermined formulation free from a powder of infiltrating material; PA0 (2) pressing the two mixes into a compact having said powder of infiltrating material present locally; PA0 (3) sintering the compact under ordinary conditions, such as heating in a cracked ammonia gas atmosphere at a temperature in the range of 1000.degree. to 1150.degree. C. PA0 (1) preparing an Fe-base powder mix which after sintering forms the principal part of a valve seat said mix further including (i) 5 to 35 wt. % of Cu, and optionally 0.01 to 4.0 wt. % of either P or Sn or both, or (ii) 5 to 35 wt. % of Cu, 0.5 to 12 wt. % of Pb, and optionally 0.1 to 4.0 wt. % of either P or Sn or both; PA0 (2) preparing another Fe-base powder mix which after sintering forms a layer to contact the valve, said mix optionally including 0.01 to 4.0 wt. % of either P or Sn or both; PA0 (3) pressing the two powder mixes to form a two-layer compact wherein one layer is composed of the first powder mix and the other layer is composed of the second powder mix. PA0 (4) sintering the two-layer compact.
Internal combustion engines such as automotive engines conventionally use a valve seat made of an Fe-base sintered material the porous area of which is infiltrated with Cu or Cu alloy in order to provide increased corrosion resistance and thermal conductivity, or an Fe-base sintered material the porous area of which is infiltrated with both Cu or Cu alloy and Pb or Pb alloy in order to provide good lubricating properties, as well as improved corrosion resistance and thermal conductivity.
However, the conventional process for producing a sintered product of Cu-infiltrated iron-base alloys is costly because a compact of infiltrating material must be prepared separately from the compact of iron-base alloy and the step of Cu infiltration must be effected after the sintering step.